Fluid streams derived from natural gas reservoirs, petroleum or coal, often contain a significant amount of acid gases, for example carbon dioxide, hydrogen sulfide, sulfur dioxide, carbon disulfide, carbonyl sulfide, hydrogen cyanide, ammonia, or mercaptans as impurities. Said fluid streams may be gas, liquid, or mixtures thereof, for example gases such as natural gas, refinery gas, hydrocarbon gasses from shale pyrolysis, synthesis gas, and the like or liquids such as liquefied petroleum gas (LPG) and natural gas liquids (NGL). Various compositions and processes for removal of acid gas contaminants are known and described in the literature.
Acid gas removal from gas streams, particularly removal of hydrogen sulfide and carbon dioxide from gas streams formed in refinery process units, synthesis gas production plants and oil and gas production facilities, is necessary to allow this gas to be used and/or sold into pipeline systems. The removal of sulfur compounds from these acid gasses or “sour gasses” is called “sweetening.”
Typically, acid gases are removed using a solvent to remove the acid gas via the production of a rich solvent. For example, it is well-known to treat such fluid streams with chemical solvents, such as amine solutions, which rely on a chemical reaction between the solvent and acid gas contaminants. The amine usually contacts the acidic gas contaminants in the fluid stream as an aqueous solution containing the amine in an absorber tower with the aqueous amine solution contacting the fluid stream counter currently. The regeneration of chemical solvents is achieved by the application of heat.
Alternatively, fluid streams may be treated with physical solvents, such as refrigerated methanol, dialkyl ethers of polyethylene glycols (DEPG), N-methyl-2-pyrrolidones (NMP), propylene carbonate, and the like which do not react chemically with the acid gas impurities. Physical solvents dissolve (absorb) the acid gas contaminants from the fluid stream, typically under high pressure. Since no chemical reactions are involved, physical solvent processes usually require less energy than chemical solvent processes. While the regeneration of chemical solvents is achieved by the application of heat, physical solvents can be stripped of impurities by reducing the pressure without the application of heat. Physical solvents tend to be favored over chemical solvents when the concentration of acid gases or other impurities is very high. Unlike chemical solvents, physical solvents are non-corrosive, requiring only carbon steel construction.
Acid gas contaminants are removed by contacting the contaminated product gas with fresh solvent in an absorber or other specialized equipment operated under conditions of high pressure and/or low temperature which are favorable for the type of solvent used. Once the contaminants are removed, the decontaminated gas is ready for sale, for use, or for additional downstream conditioning, depending on the product stream specifications. The solvent is regenerated for reuse by driving off the absorbed contaminants under low pressure and/or high temperature conditions favorable for desorption. Flash tanks and/or stripper columns are typically used to effect this separation.
While numerous prior art processes and systems for acid gas absorption and solvent regeneration are known in the art, many suffer from one or more disadvantage or inefficiency. There is an ever-existing desire to further improve these technologies, e.g., in respect of purification and energy consumption.